There are various types of scene generation systems which are used with modern vehicle or aircraft simulators and include motion film projection systems, camera model systems, and digital image generation systems. However, experience has shown that the more acceptable systems used today include camera model systems such as described in U.S. Pat. Nos. 2,975,671; 3,643,345; 3,670,426 and 3,961,133. Another acceptable visual system for use with todays modern aircraft simulators is one that produces a computer generated image such as those systems described in U.S. Pat. Nos. 3,621,214; 3,826,864 and 3,961,133.
Although the camera model system and the computer image generating system create or generate visual scenes by entirely different techniques, both of these systems may use one or more CRT's (cathode ray tubes) for presentations of the desired visual scene. In certain of these type systems, the CRT's are viewed directly, whereas in other systems the CRT's are viewed by means of optics such as beam splitters and/or mirrors. However, for certain types of applications, it has been found that the scene can better be viewed in certain simulation situations if the scene is projected onto a large panoramic or dome shaped screen surrounding (or partially surrounding) the simulator and observer. For these purposes, CRT projectors, video projectors and laser projector displays are particularly useful.
The use of projected images on a panoramic screen has been found particularly useful in certain types of aircraft simulation. To achieve a completely realistic and panoramic view for an aircraft simulator, it will be appreciated that a substantially spherical screen with a pilots eye located at or near the screen's center would be necessary. Fortunately, since the aircraft is always "below" the pilot, there is a very limited FOV (field of view) in the downward direction. Consequently, most of the panoramic screens which use a spherical screen or dome configuration need not provide a complete spherical screen in the "hemisphere" "below" the pilot since the simulator pilot has unlimited view only in the top "hemisphere". That is, assuming that the pilot's eye is fixed at or near a point at the center of the panoramic or spherical screen, it is not necessary to provide a complete bottom "hemisphere" of the screen since the aircraft itself limits the pilot's vision or FOV in the downward direction. Consequently, it has been the practice with prior art spherical screens that only the portion of the bottom hemisphere of the screen which is in the FOV or line of sight from the nominal eye "point" is provided. That is, where the "aircraft" structure itself intersects a line of sight originating from the nominal eye point it is only necessary to provide these portions of the spherical screen which are visible.
This approach has been successful for most uses, but as more and more effort is made to increase the realism of simulation systems, the limitations of this type of partial spherical screen have become apparent. For example, so long as the pilot does not move his head from the nominal eye point which is at or near the center of the spherical screen, he will have a full view provided by the visual system. However, such a fixed eye point for a pilot is not realistic since a pilot is continually turning and moving his head within the cockpit for better views and for close observation of his environment. Consequently, it has been found that when the simulator pilot moves his head to an extreme point within the cockpit such items as supports, platform walkways, and other simulator structures which are unnatural in the actual flight environment of an aircraft become apparent.
A particularly objectionable feature is the sudden intrusion of the simulator platform walkway in the pilot's FOV when he moves his head to look down over the side of the aircraft. When this occurs, it is obvious that all the effort and trouble to present the illusion of a real flight scene to a pilot may be destroyed. Therefore, since it is desirable that any training situation closely simulate the real life situation, it is essential that for effective aircraft simulation that the pilot be free to move his head with the same freedom that he would have in an actual aircraft. Further, when the pilot moves his head to an extreme position he should only be presented with the desired simulated scene and not have the illusion destroyed by the intrusion of simulator structure.
Therefore, it is an object of the present invention to provide a simple and inexpensive technique for providing a more complete panoramic view to a simulator pilot regardless of the position of the pilot's eye point.
It is still another object of this invention to provide a more complete spherical screen for a simulator visual system which readily allows maintenance to the simulator but which still provides convenience for the simulator pilot in access to and egress from the simulator.
It is yet another object of this invention to provide a more complete spherical visual screen without requiring complete redesign of the simulator support structure or the existing spherical screen.